The present invention relates to telemetering circuits and particularly to circuits designed for telemetering information from deep wells to a surface location. In the drilling and production of oil and gas wells it is necessary to transmit information relating to measurements made at the bottom of the well to a surface location. For example, in the case of producing wells, downhole-pressure surveys are periodically conducted to determine the condition of the producing formation. Downhole-pressure surveys are used to determine the extent of plugging of the formation by sand and other conditions that may decrease production.
Present bottom-hole pressures are determined by using a wireline to lower a pressure-measuring device into the well and allowing it to remain in the well for a predetermined length of time. The pressure-measuring instrument measures the pressure and records it on a self-contained recording device. After the pressure measurements are made, the instrument is withdrawn from the well and the record examined.
There have also been attempts to provide a pressure-measuring device that can be lowered into a well on a wireline which contains an electrical circuit so that the downhole pressure measurements can be transmitted to the surface where they are recorded. In the past, these instruments have consisted of an elongated instrument capsule and a two-conductor wireline circuit. The measured pressure is transmitted as an analog electrical signal to the surface where it can be recorded. The distortion in the signal in its transmission over the wireline, of course, produces a corresonding error in the pressure measurements.